This is an interesting idea. You can get instant access to your Linux desktop at anytime from within Microsoft Windows. This article will tell you everything you need to know in order to make a USB flash drive with Ubuntu Linux installed. You need:
– Obviously you need a USB flash drive (at least 2GB).
– You’ll need a working computer running Microsoft Windows with a USB port available.
– A copy of the Ubuntu 6.10 Edgy .ISO file (it’s 750MB).
– A copy of Qemu (this is the program that allows Ubuntu to actually run on Windows).
– A copy of Kqemu accelerator. This helps Qemu speed up Ubuntu.
– A copy of startubuntu.tar – This file holds two custom batch and img files.
– The HP-USB format tool to clear your USB drive.
Read rest of the procedure : How to put Ubuntu Linux on a flash drive and run it under Windows (penlinux.com)